Effect of human activities on forest ecosystems: N cycle and soil fertility

Forests are important terrestrial ecosystems, with particular nutrient cycling mechanisms to maintain structure and functions. Nitrogen is essential for forest growth and development, and commonly limited for the forest productivity. N cycles in forest ecosystems are frequently disturbed by intensive human activities. Based on a variety of research results, some potentially important human disturbances are discussed and their effects on forest ecosystems are reviewed. Precipitation is a considerable N input to forest ecosystems. However acid precipitation is detrimental to the ecosystems in the long run. Acidification causes remarkable reduction in forest productivity in the world, due to the harmful effect of acid on plant physiology and more importantly to the reduction in soil fertility by lowering mineralization and increasing N loss by runoff and leaching. The most important nutrient cycling mechanism in forest ecosystems is litterfall. Removal of trunks only for commercial use will not affect N cycle in forest ecosystems significantly, but attention on the intensity and rotation times of harvest should be paid. Clear-cutting should be prevented in forest harvesting. It deserves more attention that the change of environment after clear-cutting will affect the N cycling processes in forest ecosystems, which substantially influence soil fertility and forest productivity. Ammonification and nitrification processes are stimulated after harvesting, by which N is becoming more moveable. Unfortunately in the situation of no assimilation after clear-cutting, much of N will be lost out of the ecosystems and soil fertility will be diminished. The N pool in forest floor and underlying mineral soil is big, but forest productivity is generally low in natural conditions. Forest management is needed to meet the increasing demand for forest products. Optimization of stands structure is the most economic way to increase soil fertility and forest productivity. Mixed coniferous-broad leaved forest is recommended for plantation practice. Addition of fertilizer N effectively promotes forest productivity and may compensate for the N loss from the systems by harvesting.     

Are Partial Nutrient Balances Suitable to Evaluate Nutrient Sustainability of Land use Systems? Results from a Case Study in Central Sulawesi,Indonesia

Nutrient input–output balances are often used as indicators for the sustainability of land use systems. In a case study on plot scale in Central Sulawesi, Indonesia, we measured nutrient input–output balances of natural rainforest and two unfertilized land use systems (maize, and coffee/cacao agroforestry). These are the two major land use systems on converted rainforest sites in this part of Sulawesi. We wanted to test if (a) plant nutrient balances are negative, (b) which pathway is most important for losses of plant nutrients, and (c) if partial plant nutrient balances are suitable to evaluate sustainability of the land use systems. We measured nutrient inputs by precipitation and nutrient outputs by harvest export and leaching. We selected two locations, the first was situated on a fertile Cambisol developed on alluvial sediment soil, and the second on a less fertile Cambisol developed on weathered phyllite substrate. Nutrient losses through leaching were higher on sites with higher soil fertility. Nutrient balances in natural forest on fertile soils were negative for N, Ca, K and Mg. Inputs of P by precipitation and outputs by leaching were below detection limit. On less fertile soils, leaching of N and K in natural forest was lower than inputs by precipitation. As net nutrient losses were highest in agroforestry, followed by maize and natural forest stands, forest conversion into agricultural land will result in increased nutrient losses. Main output pathway of N, P and K was harvest, whereas main output pathway for Ca and Mg was through leaching. The annual losses of nutrients we measured were higher than in comparable studies on nutrient poor soils; however losses were only small fractions of available nutrient stocks. Our results showed negative partial nutrient balances in both agricultural systems. Nutrient balances in this study were more influenced by native soil fertility than by land use. Because we found indirect evidence that some nutrient pathways, which were not measured, may have significantly changed the overall balance (biological N fixation, weathering), we conclude that partial nutrient balances are no good indicators for sustainability of land use systems.     

Atmospheric ammonia and ammonium transport in Europe and critical loads: a review

The atmosphere in Europe is polluted by easily available nitrogen (ammonium and nitrate) mainly from livestock (NH₃), traffic (NO_x) and stationary combustion sources (NO_x). The nitrogen emission from various European sources decreases in the order: agriculture, road traffic, stationary sources and other mobile sources (including vehicular emissions from agriculture), with annual emissions of approximately 4.9, 2.7, 2.7 and 0.8 Mt N respectively. The emissions have increased dramatically during the latest decades. In the atmosphere the pollutants are oxidised to more water soluble compounds that are washed out by clouds and eventually brought back to the earth's surface again. Since ammonia is emitted in a highly water soluble form it will also to a substantial degree be dry deposited near the source. Ammonia is, however, the dominant basic compound in the atmosphere and will form salts with acidic gases. These salt particles can be transported long distances especially in the absence of clouds.The deposition close to the source is substantial, but hard to estimate due to interaction with other pollutants. Far from the source the deposition of ammonium is on an annual average halved approximately every 400 km. This short transport distance and the substantial deposition near the source makes it possible for countries to control their ammonium deposition by decreasing their emissions, provided that there is no country with much higher emission in the direction of the prevailing wind trajectory. When the easily available nitrogen is deposited on natural ecosystems (lakes, forests), negative effect can occur. The effect is determined by the magnitude of the deposition and the type of ecosystems (its critical load for nitrogen). In order to reduce the negative effects by controlling the emissions in a cost-efficient way it is necessary to use atmospheric transport models and critical loads.     

Simulation of the dynamics of nutrients and moisture in tropical ecosystems

In tropical rain forests, tree growth is often limited by scarcity of nutrients. For the study of the effects of nutrients and moisture on growth, the use of models is almost compulsory. The main output of the models discussed, NUTCYC and DYNAMITE, is the growth of forest vegetation and, in case of shifting cultivation, also the yields of agricultural crops.State variables, water and nutrient flows, nutrient uptake, growth of the vegetation and required input data are shortly described. Sensitivity analysis identified retranslocation of nutrients in the vegetation as one of the major growth determining processes. As a demonstration of the use of such models, rice yields are calculated that can be expected under various shifting-cultivation scenarios. Finally the models are briefly evaluated, and some questions are discussed that arose when the models were developed.     

Nitrogen fertilizer equivalencies of organics of differing quality and optimum combination with inorganic nitrogen source in Central Kenya

Decline in crop yields is a major problem facing smallholder farmers in Kenya and the entire Sub-Saharan region. This is attributed mainly to the mining of major nutrients due to continuous cropping without addition of adequate external nutrients. In most cases inorganic fertilizers are expensive, hence unaffordable to most smallholder farmers. Although organic nutrient sources are available, information about their potential use is scanty. A field experiment was set up in the sub-humid highlands of Kenya to establish the chemical fertilizer equivalency values of different organic materials based on their quality. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonia), Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with %N>3) obtained from hedgerows grown ex situ (biomass transfer) and urea (inorganic nitrogen source) were applied. Results obtained for the cumulative above ground biomass yield for three seasons indicated that a combination of both organic and inorganic nutrient source gave higher maize biomass yield than when each was applied separately. Above ground biomass yield production in maize (t ha^–1) from organic and inorganic fertilization was in the order of senna+urea (31.2), tithonia+urea (29.4), calliandra+urea (29.3), tithonia (28.6), senna (27.9), urea (27.4), calliandra (25.9), and control (22.5) for three cumulative seasons. On average, the three organic materials (calliandra, senna and tithonia) gave fertilizer equivalency values for the nitrogen contained in them of 50, 87 and 118%, respectively. It is therefore recommended that tithonia biomass be used in place of mineral fertilizer as a source of nitrogen. The high equivalency values can be attributed to the synergetic effects of nutrient supply, and improved moisture and soil physical conditions of the mulch. However, for sustainable agricultural production, combination with mineral fertilizer would be the best option.     

建立灌木能源林概念并构筑林业可再生能源新产业链

在探讨我国发展生物质能源重要意义的基础上,分析了灌木林既具有较高的生态功能和经济价值,同时也可培育成优良的能源林.根据西部地区的特点,可结合生态环境建设加强灌木林营造,发展灌木能源林.     

Dynamics of soil nutrients and microbial biomass during first year cropping in an 8-year jhum cycle

The soil nutrient status and microbial biomass at three stages of firstyear cropping in an 8-year jhum (slash-and-burn agriculture) cycle system weredetermined and compared to an adjacent humid tropical forest in ArunachalPradesh, north-eastern India. Soil pH increased after burning and decreased asthe cultivation progressed in the jhum field. Soil organic carbon, available-P,total Kjeldahl nitrogen, ammonium-N and nitrate-N decreased as the duration ofcultivation increased. Microbial biomass C, N, and P were high in the foreststand. Microbial biomass C increased gradually as cultivation progressed, whilemicrobial biomass N and P showed a post-burn decreasing trend. Bacterial andfungal populations were drastically reduced following slash burning. The studyindicates that first-year cropping may result in temporary patternhomogenization of soil nutrient cycling, but can have drastic effects withcontinued slashing and burning for long-term agriculture.     

Fertilizers and eutrophication in southwestern Australia: Setting the scene

An excess of plant nutrients has caused serious eutrophication in aquatic ecosystems of southwestern Australia manifested by excessive growth and accumulation of green and bluegreen algae. Phosphorus is generally the limiting nutrient for algal growth and phosphatic fertilizers applied to nutrient-deficient, leaching, sandy soils are the main source of P, supplemented by rural industry point sources. Nitrogen is the limiting nutrient in marine embayments with little drainage from the land. Measures to reduce the load of P delivered to drainage include basing fertilizer application rates on soil testing for P and the use of less soluble P fertilizers. Catchment management plans are being implemented with community involvement to reduce P loads and maintain agricultural production. This introductory paper reviews the history of eutrophication in southwestern Australia and of studies into its causes, principally in the large Peel-Harvey estuary. It briefly summarises other papers in this special issue concerned with different aspects of the problem: how to fertilize the land without causing eutrophication.     

Retention and leaching of N in Norwegian coniferous forests

Nitrogen is brought into natural ecosystems from the atmosphere through N-fixation and deposition of NH ₄ ⁺ and NO ₃ ^- as wet and dry deposition. N is lost from terrestrial ecosystems unaffected by human activities by leaching or as gas, but the losses from different forest-and vegetation types are poorly quantified. The leaching is hampered by uptake in the vegetation and by immobilisation by soil organisms. The gas loss of N in the form of N₂O and N₂ appears to be rather small, but the loss of NO is unknown. Human activities such as those leading to the increased atmospheric dry and wet deposition of N, may affect the N-losses, but the increase in losses are likely to be very dependent on the amounts of N deposited. The present paper discusses the fate of the N deposited under the existing pollution climate in Norway where N deposition above the natural background has taken place for at least 50 years. The deposition today varies from about 15–20 kg N ha^-1 yr^-1 in the southernmost parts of the country to background values of about 2 kg ha^-1 yr^-1 in the north. Even in areas with the highest loads there are no clear indications that N-leaching in forest ecosystems has increased to unacceptable levels. The main reason for this appears to be that most of the N deposited are immobilised in forest soils and utilised by forest trees and ground cover vegetation to increased biomass production. At present therefore, no clear signs of N-saturation can be found. This is in relatively good accordance with estimates of critical loads for N in Norwegian coniferous forests. Estimates of immobilisation, gas losses, net uptake in vegetation, biological fixation as well as a figure for acceptable leaching, indicate that the long-term critical load of N might be of the order 10 to 30 kg N ha^-1 yr^-1. Most of the N deposited from the atmosphere appears therefore so far to be retained in the forests and only a small proportion seems to be lost to ground-and surface waters.     

Food production and consumption in Germany: N flows and N emissions

During the past four decades the authors perceive that an increasing non-sustainability (Disintegration) within the agriculture , human nutrition, waste management complex has occurred both in Germany and the European Union. Compared to the basic needs of the population for nutritive energy, fat and protein, we estimate that the production and consumption of food and feed is more than 50% higher than necessary. Using nitrogen (N) input into German agriculture in 1991/92 as an example, we estimated that the N input of 191 kg ha^-1 was 2 to 3 times too high. This high N input resulted in the net biomass production of 45 kg ha^-1, a 25% efficiency. This inefficiency causes emissions of reactive N and other nutrient compounds into the hydrosphere and atmosphere that were 2 to 8 times too high. For example the contributions of agriculture to the total annual N₂O–N emissions of Germany (during 1990–1992), Europe (1990) and of the world (1989) were 110, 691 Gg and 6.7 Tg or 52, 62 and 41%, respectively. The authors demonstrate that emissions of N and P from Germany and EU waste water management systems are also higher than necessary because nutrient recycling is not practiced extensively. Excessive food production and consumption has made the agriculture/human nutrition/waste and waste water complex, like the energy/transportation complex, a main cause of new transboundary environmental damage such as soil and water acidification, hypertrophication of near-natural terrestrial and aquatic ecosystems and climate change.We propose that a sustainable food production/consumption system can be developed that is based both on need-oriented production and consumption with no net exports and on recovery, recycling and more efficient use of nutrients. Using N as an example, the authors show which short and long term action aims must be set and realized by the year 2015, to meet environmental, economical and social sustainability requisites. The suggested, assumed sustainable N balance for German agriculture is characterized by a critical annual input and surplus maximum of 80 and 45 kg N ha^-1 respectively, which should almost double biomass production efficiency for N utilization. This estimate is based on reducing animal stocking rates to 0.5 gross weight unit ha^-1 to attain no net mineralization or immobilization of N in the soil.     

Multiple benefits of manure: The key to maintenance of soil fertility and restoration of depleted sandy soils on African smallholder farms

Manure is a key nutrient resource on smallholder farms in the tropics, especially on poorly buffered sandy soils, due to its multiple benefits for soil fertility. Farmers preferentially apply manure to fields closest to homesteads (homefields), which are more fertile than fields further away (outfields). A three-year experiment was established on homefields and outfields on sandy and clayey soils to assess the effects of mineral nitrogen (N) fertilizer application in combination with manure or mineral phosphorus (P) on maize yields and soil chemical properties. Significant maize responses to application of N and manure were observed on all fields except the depleted sandy outfield. Large amounts of manure (17 t ha⁻¹ year⁻¹) were required to significantly increase soil organic carbon (SOC), pH, available P, and base saturation, and restore productivity of the depleted sandy outfield. Sole N as ammonium nitrate (100 kg N ha⁻¹) or in combination with single superphosphate led to acidification of the sandy soils, with a decrease of up to 0.8 pH units after three seasons. In a greenhouse experiment, N and calcium (Ca) were identified as deficient in the sandy homefield, while N, P, Ca, and zinc (Zn) were deficient or low on the sandy outfield. The deficiencies of Ca and Zn were alleviated by the addition of manure. This study highlights the essential role of manure in sustaining and replenishing soil fertility on smallholder farms through its multiple effects, although it should be used in combination with N mineral fertilizers due to its low capacity to supply N.     

The role and function of organic matter in tropical soils

Soil organic matter (SOM) has many functions, the relative importance of which differ with soil type, climate, and land use. Commonly the most importantfunction of OM in soil is as a reserve of the nitrogen and other nutrients required by plants, and ultimately by the human population. Other important functions include: the formation of stable aggregates and soil surface protection; maintenance of the vast array of biological functions, including the immobilization and release of nutrients; provision of ion exchange capacity; and storage of terrestrial carbon (C). This paper considers the quantity and quality of SOM of soils in the tropics, which are estimated to contain one quarter of the C in the global pool in terrestrial soils, and supports strongly the use of analytical methods to characterizing labile SOM to develop valuable insights into C dynamics. As in other regions, the transformation of tropical lands for agriculture exploits SOM, and in particular nutrient reserves. The process of exploitation is accelerated in the tropics by the necessity to increase agricultural production, largely through agricultural intensification, to overcome inadequate nutrition, to satisfy population growth, and to cope with the limited reserves of arable land. Poverty has an overriding influence on the exploitation and degradation processes. Areas at greatest risk of land degradation are the infertile acid soils of the tropics, which, invariably, are cultivated by the poor. Soil organic matter has a central role in sustainable land management, but perspectives on the roles of SOM differ widely between farmers, consumers, scientists and policy-makers. Some consider SOM as a source of nutrients to be exploited, whereas others can afford to utilize it as a key component in the management of the chemical, biological, and physical fertility of soils. Still others see SOM as a dumping ground for excess nutrients and toxins, or as a convenient store for fossil fuel emissions, particularly CO₂. Farmers need sustainable land management systems that maintain OM and nutrient reserves. Nevertheless, many available practices, whether based on indigenous or scientific knowledge, do not meet social and economic criteria that govern farmer behaviour. Much scientific knowledge about the various roles of SOM does not reach farmers and other decision-makers in a form that can be used easily. The biggest challenge to researchers is to engage with clients to pinpoint gaps in knowledge and utilize new and existing information to devise decision support Systems tailored to their needs. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of different land-cover types on the changes of selected soil properties in the mountain region of Rawalakot Azad Jammu and Kashmir

The study focused on the impact of change in land-cover types on soil quality inferred by measuring the relative changes in chemical and physical properties of non-disturbed and disturbed soil system. Soil samples were collected from major land-cover types in the mountain region: natural forest, grassland and cultivated land (arable). The natural forest served as a control against which to assess changes in soil properties resulting from the removal of natural vegetation or cultivation of soil. Soil samples were collected from 0–15 and 15–30 cm depth six times during the year and examined for their nutrient status, i.e. soil organic matter (SOM); total N (TN); available P (AP); available K (AK); cation exchange capacity (CEC), pH and physical properties like particle size distribution, bulk density (BD), and porosity. Significant differences among land-cover types were found for SOM, TN, AP; AK, CEC and pH. Soil collected from the forest had the highest levels of all nutrients followed by grassland while soil from the arable site had very low nutrient status indicated an extractive effect of cultivation and agricultural practices on soil. With significantly lower clay contents (20%), texturally the soil of arable site was quite different from that of the natural forest and grassland. Similarly, a 13% more BD and 12% lower porosity showed structural deterioration of arable soil. The changes in clay contents, BD and porosity due to cultivation suggest adverse effects on environmental protection functions of soil. The correlation coefficient between OM to TN, AP, AK and CEC suggesting that within a narrow range of soil, OM may serves as a suitable indicator of soil quality. Natural vegetation appeared to be a main contributor of soil quality as it maintained the organic carbon stock and increased the nutrient status of soil and is therefore, important to sustain high-altitude ecosystems and reinstate the degraded lands in the mountain region.     

Emission of nitrous oxide from soils used for agriculture

Nitrous oxide is emitted into the atmosphere as a result of biomass burning, and biological processes in soils. Biomass burning is not only an instantaneous source of nitrous oxide, but it results in a longer term enhancement of the biogenic production of this gas. Measurements of nitrous oxide emissions from soils before and after a controlled burn showed that significantly more nitrous oxide was exhaled after the burn. The current belief is that 90% of the emissions come from soils. Nitrous oxide is formed in soils during the microbiological processes nitrification and denitrification. Because nitrous oxide is a gas it can escape from soil during these transformations. Nitrous oxide production is controlled by temperature, pH, water holding capacity of the soil, irrigation practices, fertilizer rate, tillage practice, soil type, oxygen concentration, availability of carbon, vegetation, land use practices and use of chemicals. Nitrous oxide emissions from agricultural soils are increased by the addition of fertilizer nitrogen and by the growth of legumes to fix atmospheric nitrogen. A recent analysis suggests that emissions of nitrous oxide from fertilized soils are not related to the type of fertilizer nitrogen applied and emissions can be calculated from the amount of nitrogen applied. Legumes also contribute to nitrous oxide emission in a number of ways, viz. atmospheric nitrogen fixed by legumes can be nitrified and denitrified in the same way as fertilizer nitrogen, thus providing a source of nitrous oxide, and symbiotically living Rhizobia in root nodules are able to denitrify and produce nitrous oxide. Conversion of tropical forests to crop production and pasture has a significant effect on the emission of nitrous oxide. Emissions of nitrous oxide increased by about a factor of two when a forest in central Brazil was clear cut, and pasture soils in the same area produced three times as much nitrous oxide as adjacent forest soils. Studies on temperate and tropical rice fields show that less than 0.1% of the applied nitrogen is emitted as nitrous oxide if the soils are flooded for a number of days before fertilizer application. However, if mineral nitrogen is present in the soil before flooding it will serve as a source of nitrous oxide during wetting and drying cycles before permanent flooding. Thus dry seeded rice can be a source of considerable nitrous oxide. There are also indirect contributions to nitrous oxide emission through volatilization of ammonia and emission of nitric oxides into the atmosphere, and their redistribution over the landscape through wet and dry deposition. In general nitrous oxide emissions can be decreased by management practices which optimize the crop's natural ability to compete with processes whereby plant available nitrogen is lost from the soil-plant system. If these options were implemented they would also result in increased productivity and reduced inputs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Macro and micro-nutrient effects on the yield and nutrient concentration of maize (Zea mays L.) in South Western Nigeria

Despite various fertilizer recommendations, maize (Zea mays L.) yields in tropical forest and savanna zones are very low. These low yields could be attributed in part to the exclusion of some secondary and all micro nutrients in fertilizer recommendations for maize, a condition which often leads to nutrient imbalance. The inclusion of some secondary and micro nutrients in fertilizer recommendation for successful maize cultivation in this zone has been suggested [2, 16] but no one has proposed a balanced nutrient program for this purpose. Field trials were therefore conducted to investigate the potential for improving maize yields by fertilizing soils of different parent materials with both macro and micro nutrients in three ecological zones of maize production in south western Nigeria.The study has indicated that in addition to NPK, Mg was necessary for high yield of maize on forest soils derived from sedimentary materials while on forest and savanna soils formed from basement complex rocks, inclusion of Mg, Fe, Cu and Zn to NPK was required. This was further confirmed with ear leaf tissue and soil analyses. High nutrient concentration in earleaf does not necessarily guarantee high yield of maize. It is therefore concluded that there is a need for soil testing program in this region.     

Soil nutrient depletion by agricultural production in Southern Mali

The degree of soil mining by agricultural production in Southern Mali is assessed by calculating nutrient balances: differences between the amount of plant nutrients exported from the cultivated fields, and those added to the fields. Export processes include extraction by crops, losses due to leaching, to erosion, and to volatilization and denitrification. Inputs include applications of fertilizer and manure, restitution of crop residues, nitrogen fixation, atmospheric deposition of nutrients in rain and dust, and enrichment by weathering of soil minerals. Nutrient balances are calculated for N, P, K, Ca, and Mg. Both pessimistic and optimistic estimates are given.The resulting figures indicate, even when the most optimistic estimates are used, large deficits for nitrogen, potassium and magnesium. For the region as a whole, the calculated deficits are -25 kg N/ha,-20 kg K/ha, and -5 kg Mg/ha. Further, acidification is to be expected, in particular in areas where cotton is grown. The deficits are caused by traditional cereal crops, but also by cotton and especially by groundnut. The latter two crops are fertilized, but insufficiently. It is important to note, that the negative figures are not automatic recommendations for application of a specific amount of additional fertilizer. For phosphorus and calcium the balance of the region as a whole appears to be about in equilibrium, but locally large variations may occur.Erosion and denitrification are important causes of nutrient loss, accounting respectively for 17 and 22% of total nitrogen exports. Atmospheric deposition and weathering of minerals in the soil are still important nutrient inputs that contribute as much as nutrients as organic and mineral fertilizer combined. Nutrient depletion is very large in comparison to the amount of fertilizer applied. Drastic options, such as doubling the application of fertilizer or manure, or halving erosion losses, even if feasible, would still not be enough to make up for the calculated deficits.The annual value of withdrawn nutrients, if related to prices of fertilizers, varies between 10,000 and 15,000 FCFA/ha (40-60 US $/ha). Since the estimated average gross margin from farming in this area is 34,000 FCFA/ha (123 US $/ha), soil mining appears to provide an amount equal to 40% of farmers' total income from agricultural activities.     

On the reason why acid treatment of biomass enhances the biosorption capacity of cationic pollutants

The present work is aimed at understanding the effect of acid treatment and demonstrating the reason for its effect. For this, Corynebacterium glutamicum biomass was used as a model biomass. Two cationic (cadmium and Methylene Blue) and one anionic (Reactive Red 4) pollutants were used to evaluate the sorption capacity by the biomass. Isotherm experiments showed that acid treatment of the biomass increased the uptake of the cationic pollutants, but decreased that of the anionic pollutant. Through the results of FTIR and potentiometric titrations, it was found that carboxyl groups on the biomass increased after acid treatment. The carboxyl groups seem to be generated likely through hydrolysis of esters in the biomass under the acidic condition. Therefore, increase of the carboxyl groups provided the binding sites for cationic pollutants, whereas it may interfere with the binding of anionic pollutants.     

垂直碳纳米管阵列的生长控制研究进展

垂直碳纳米管（VACNT）阵列由于具有良好的排列、优异的导电导热能力、高比表面积、高纯度等优点而得到广泛应用。本文概述了用于碳纳米管阵列生长的热化学气相沉积（CVD）制备方法的最新进展,重点阐述了CVD法生长碳纳米管阵列的动力学与生长终止机理,指出CVD过程中的催化剂形貌演化是引发碳纳米管阵列生长停止的重要原因。介绍了人们通过生长条件控制与催化剂设计等方法调控碳纳米管阵列结构（包括管壁数、管径和密度）方面取得的进展,指出碳纳米管阵列的大批量制备及结构参数的精确调控是未来发展的 重点。     

Silicon Mobilization in Soils: the Broader Impact of Land Use

Dissolved Si (DSi) provision from land systems triggers diatom growth and CO₂ sequestration. Soils and ecosystems act as a Si “filter”, transforming DSi originated from mineral weathering into biogenic Si (BSi) after DSi uptake by plants, or into other pedogenic forms of Si (non-BSi). Land use changes the quantity of BSi and non-BSi pools along the soil profile. However, methods used to isolate Si pools include chemical extractions at high temperatures and alkaline environments and therefore are unable to provide information concerning the dissolution potential of BSi and non-BSi pools under normal conditions of temperature and pH. Here, we conducted a batch experiment where forest, pasture and cropland soil samples were mixed with water at 25 °C and pH 7. The soil samples were collected from a temperate land use gradient located in the Belgian Loess Belt. We measured dissolved Si and aluminium (Al) during 80 days. BSi and non-BSi pool contents along the soil profile were known, as they had been established previously through chemical extraction. Results show that BSi and non-BSi enriched samples present distinct Si and Al dissolution curves. While non-BSi pools contribute significantly with immediate availability of Si, BSi pools present an initial slow dissolution. Therefore, croplands that were depleted of phytoliths and had poorly organic horizons display higher concentrations of initial dissolved Si, while pastures and forests, where pedogenic pools dominate only at depths below 40 cm, have more limited initial Si release.

     

Crop yield and the fate of nitrogen and phosphorus following application of plant material and feces to soil

Organic materials are the most important sources of nutrients for agricultural production in farming systems of semi-arid West Africa. However, reliance on locally available organic nutrient sources for both crop and livestock production is rapidly becoming unsustainable. A series of feeding and agronomic trials have been conducted to address the role of livestock in sustainable nutrient cycling. This paper reports results of a greenhouse study that evaluated the effects of applying crop residue and browse leaves, or feces derived from these feeds, at equal organic-N application rates (150 kg ha^-1), alone or with fertilizer-N (60 kg ha^-1), on pearl millet (Pennisetum glaucum [L.] R.Br.) dry matter (DM) yield, nitrogen (N) and phosphorus (P) uptake, on soil nutrients, and on total, labile and recalcitrant fractions of soil organic matter (SOM). Millet DM and cumulative N uptake were most affected by fertilizer-N, followed by plant species and amendment type, although various interactions among these treatments were noted due to variations in the composition of the applied amendments. Fertilizer-N increased total millet DM by 39%, N uptake by 58% and P uptake by 17%, and enhanced N mineralization from most organic amendments, but was applied insufficiently to totally offset N and P immobilization in pots containing leaves of low initial N and P content. Feces alone appeared to supply sufficient N to meet millet-N demands. Nitrogen use efficiency was, in most cases, higher in pots amended with feces than with leaves. Nitrogen in feces apparently mineralized more in synchrony with millet-N demands. Also, the relatively high cell wall content of feces may have provided an effective, temporary sink for fertilizer-N, which upon remineralization provided more N to millet than pots amended with leaves. Whereas most of the P contained in feces mineralized and was taken up by millet, most leaves immobilized P. Assessing the costs and benefits associated with the direct land application of biomass as a soil fertility amendment versus feeding biomass first to livestock then using feces (and urine) to fertilize the soil requires information on both crop and livestock production and associated impacts on nutrient cycling.